A broad array of infant studies are reviewed that appear to be consistent with the idea that belief understanding specifically, and mental attribution generally, emerge much earlier than previously acknowledged. We first examine existing false-belief research, which, while confirming that children under 4 years perform poorly on standard tests, suggests nevertheless that they have more implicit understanding of beliefs than they can express. After surveying theories that both favor and reject early development of theory of mind (TOM), we address two recent bodies of visual fixation research that provide support for the possibility of knowledge and belief attribution in infancy. The first indicates that infants of 13-15 months are sensitive to others' false beliefs (and therefore have a representational TOM), the second, that by 12 months or younger infants have two antecedently related psychological understandings: (a) that when agents look they "see" and (b) that seeing plays a presumptive role in producing knowledge. This raises the broader question of whether "mentalism" might be part of core knowledge, which takes us to the earliest manifestation of psychological attribution, the construal of agentive behavior as intentional. Contrary to previous assumptions, recent studies indicate that infants of 3-9 months do not accord intentionality exclusively to humans or to self-propelled objects but rather to any entity that: (1) chooses flexibly among means and ends, (2) responds non-randomly to social overtures, and (3) reacts rationally to changing circumstances (i.e., that is not a mere automaton but is selectively and adaptively responsive to the environment). Other evidence is then examined which suggests that infants begin to construe these and other behaviors in mentalist rather than teleological terms much earlier than expected. Finally, the implications of this empirical record for domain-specific and domain-general theories of TOM are considered.